The present invention relates to a modular plug for a cable having a plurality of wires, the plug comprising a housing with a wire receivable cavity adapted for guiding ends of the cable wires towards a contact end of said modular plug.
Such a modular plug is generally known in the art, it is for instance a standardized RJ45 [Registered Jack] data transmission plug widely used in telecommunications and data interconnection systems. A common problem with this kind of plug is to satisfy always-increasing data transmission speeds, while maintaining production costs as low as possible. To this end, and in order to achieve data transmission rates required by certain standard values desired in many applications (e.g. Category 6, Category 7, in LAN (Local Area Networks)), the design of the modular plug is constantly improved. One of these improvements is for instance described in the European Patent Application EP-A2-0 716 477 by Bofill et al, and entitled xe2x80x9cModular plug for high speed data transmissionxe2x80x9d. Therein, a wire holder is provided for being inserted in a cavity of the plug. The wire holder is used for arranging and holding the wires of twisted pairs in a predetermined order and to bring, when inserted in the plug, the ends of the wires in a position proximate to a zone of contact where plug contacts can be connected to the wires. The plug contacts are provided with insulation piercing parts that are pressed to pierce through the insulation or the wires in order to contact the conducting strands thereof.
In this known plug, the wires of the pairs are maintained twisted in the wire holder and the length of the straightened or untwisted wire ends is as short as possible. The object thereof is to minimize the well-known cross talk effect caused by electromagnetic interferences between the conductors. However, the insulation piercing parts are relatively large parallel plates facing each other, thereby creating unwanted high capacitive effects that negatively affect the quality of the connector.
On the other hand, in order to remain advantageous in comparison to any other data connector for transmission of high-speed data, the modular plug needs to be produced at relatively low cost.
In order to reduce the number of components and thus the cost of electrical connectors for medical instrumentation, documents U.S. Pat. Nos. 6,010,371 and 5,564,951 both describe an electrical connector having a plurality of wires, and comprising a housing with a cavity adapted for guiding the ends of cable wires towards a contact end of the connector. The contact end of the connector is provided with a plurality of grooves adapted for receiving the bared ends of the wires, portions of these bared ends forming contact terminals of the conductor.
The problem with this type of connectors is that it is not adapted for very high bit rate transmission. Indeed, for connectors to be used in very high bit rate applications, it is of the utmost importance to avoid capacitive effect between adjacent contact terminals. In the connectors of the type mentioned above, the parts of the wires which are parallel to each other are quite long, which increases the capacitive effect between the ends of adjacent wires and is thus detrimental to the transmission characteristics of the connector at very high bit rates. This is because the contact portion of the bared wires forms an angle of about 180xc2x0 with the portion of the wire that enters the housing.
In addition, it is necessary to have a complex molding of the housing in order to receive the contact portion that is rotated 180xc2x0 with respect to the portion of the bared wire that enters the housing.
An object of the present invention is to provide a modular plug of the known type but whereof the production cost is dramatically low while being adapted to achieve a connection to a cable for use in high-speed data transmission applications with reduced cross talk.
According to the invention, this object is achieved due to the fact that the contact end of said modular plug is provided with a plurality of grooves adapted for receiving bared ends of said wires, portions of said bared ends forming contact terminals of said modular plug, the angle between each of said portions forming a contact terminal and the portion of said bared end that is located between the portion forming a contact terminal and the insulated part of the wire is less than 90xc2x0.
In this way, the portions of the bared wire ends of the cable that define directly the contact terminals of the modular plug do not have an excessive length in parallel so that the capacitive effect is much more limited than with the prior art.
Besides, the present plug is easier to manufacture than the ones of the prior art.
In addition, the contact can be made directly at the contact end of the modular plug.
At last, the plug of the invention is cost-effective because there is no wire holder required, nor plug contact with insulation piercing parts. The removal of the plug contacts not only reduces dramatically the production cost of the modular plug, but also reduces the cross talk effect. Indeed, the plug contacts comprising the insulation piercing parts and constituted by relatively large metallic plates facing each other with a close spacing, resulting in large capacitors, are no longer present.
Moreover, since the wire receivable cavity is only used for guiding the ends of the wires towards the contact end of the plug, the length of this cavity may be reduced to a minimal value to reduce even more the unwanted cross talk effect.
According to an additional feature of the invention, the angle between the portion of said bared end located between the portion forming a contact terminal and the insulated part of the wire, and said insulated part of the wire, is less than 90xc2x0.
In a preferred embodiment of the present invention, said housing has a fixed part and a removable part, said fixed part having a first wall of the plug housing cavity and said removable part having a second wall, opposite to said first wall, of said plug housing cavity, said first and second walls being adapted to cooperate for holding the wire ends into said plug housing cavity.
In this way, the ends of the cable may be prepared to fit exactly into the modular plug and to be positioned into the fixed part of the plug prior to mount the removable part there over. This is preferable than inserting by sliding the several straightened wire ends into the wire receivable cavity and then pushing these ends into the grooves while watching that the correct wire order is maintained.
Another characterizing embodiment of the present invention is that said housing is further provided with a plurality of blind holes substantially orthogonal to said grooves, said holes being located at ends of the grooves and being adapted for receiving tips of the bared wire ends.
The bared wire ends are so maintained with a tight fit in the grooves between the plug housing cavity and the blind holes. By holding the tips of the wires in the holes, these wires are prevented to move within the grooves and the quality of the contact terminals created thereby is increased.
Also another characterizing embodiment of the present invention is that each wire of the cable is an insulated single conductor wire.
Single conductor wires are preferred over braided multi-conductor wires because of their rigidity used to constitute contact terminals.
Another object of the present invention is to provide a cost effective method of coupling a cable, e.g. with twisted wire pairs, to a modular plug according to the invention in order to provide an arrangement having a relatively low cross talk effect and thus usable in high speed applications.
According to the invention, this other object is achieved due to the fact that said method comprises steps of:
arranging the ends of the wires of the cable in a single plane;
baring and straightening the ends of the wires over a predetermined length;
positioning the wire ends in a wire receivable cavity of a housing of said modular plug; and
positioning the bared wire ends in wire receiving grooves located at a contact end of said modular plug, portions of said bared wire ends forming so contact terminals of said modular plug.
By using bared end of the wires of the cable as contact terminals rather than the classical metallic plug contacts, the arrangement is relatively economic to produce. Furthermore, the cross talk effect resulting from the close juxtaposition of large metallic plates constituting the known plug contacts is removed.
In a preferred embodiment of the present invention, the housing of said modular plug has a fixed part and a removable part, and said method comprises further steps of:
positioning the wire ends against a first wall of said fixed part of the modular plug;
positioning the bared wire ends with a tight fit into said wire receiving grooves so that longitudinal portions of the bared wire ends extend outside said grooves to form contact terminals of said modular plug; and
mounting said removable part onto said fixed part of the modular plug so that a second wall provided by said removable part is positioned against said wire ends in order to hold said wire ends into a wire receivable cavity delimited by said first and said second walls.
In this way, the wire ends may be prepared to fit exactly into the fixed part of the modular plug, with the bared portion fitting into the grooves. The next and final step is then to mount the removable part over the positioned wires. This is easier than inserting the many wire ends into the wire receivable cavity and then pushing the straightened wire ends into the grooves.
Another characterizing embodiment of the present invention is that said method further comprises steps of:
upwards bending the tips of the bared wire ends orthogonally to said wire receiving grooves; and
engaging said tips into holes provided at ends of said grooves.
By holding the wire tips in the holes, the bared wire ends are prevented to move within the grooves and the quality of the contact terminals is increased.
It is to be noted that the present method of coupling a cable to a modular plug perfectly suits to the above modular plug of the invention.
Further characterizing embodiments of the present modular plug and method are mentioned in the appended claims.
It is to be noticed that the term xe2x80x98comprisingxe2x80x99, used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression xe2x80x98a device comprising means A and Bxe2x80x99 should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.